Diffraction grating with a variable refractive index formed using an energy gradient

ABSTRACT

An optical device with a variable index of refraction is formed by exposing a film to an energy gradient. The optical device has angular selectivity. The optical device can be used as an output coupler for a waveguide used in a virtual-reality and/or augmented-reality apparatus.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. Non-Provisional applicationSer. No. 15/878,230, filed Jan. 23, 2018, titled “Diffraction Gratingwith a Variable Refractive Index Formed Using an Energy Gradient,” whichis herein incorporated herein by reference in its entirety. Thefollowing three U.S. patent applications (including this one) were filedconcurrently, and the entire disclosure of the other applications areincorporated by reference into this application for all purposes:

application Ser. No. 15/878,227, filed Jan. 23, 2018, entitled“Diffraction Grating with a Variable Refractive Index Using MultipleResins”;

application Ser. No. 15/878,230, filed Jan. 23, 2018, entitled“Diffraction Grating with a Variable Refractive Index Formed Using anEnergy Gradient”; and

application Ser. No. 15/878,232, filed Jan. 23, 2018, entitled“Diffraction Grating with a Variable Refractive Index Using IonImplantation.”

BACKGROUND

The disclosure relates generally to near-eye-display systems, and morespecifically to waveguide displays with a small form factor, a largefield of view, and/or a large eyebox. Near-eye, light-field displaysproject images directly into a user's eye, encompassing both near-eyedisplays and electronic viewfinders. Conventional near-eye displaysgenerally have a display element that generates image light that passesthrough one or more lenses before reaching a user's eyes. Additionally,near-eye displays in virtual-reality (VR) systems and/oraugmented-reality (AR) systems have design criteria to be compact, belightweight, and provide two-dimensional expansion with a large eyeboxand a wide field-of-view (FOV). In typical near-eye displays, a limitfor the FOV is based on satisfying two physical conditions: (1) anoccurrence of total internal reflection of image light coupled into awaveguide, and (2) an existence of a first-order diffraction caused by adiffraction grating. Conventional methods used to satisfy the above twophysical conditions rely on heavy and expensive components. Further,designing a conventional near-eye display with two-dimensional expansioninvolving two different output-grating elements that are spatiallyseparated often results in a large form factor. Accordingly, it ischallenging to design near-eye displays using conventional methods toachieve a small form factor, a large FOV, and/or a large eyebox.

SUMMARY

The present disclosure relates generally to an optical device with avariable index of refraction. More specifically, and without limitation,this disclosure relates to an optical grating with a variable index ofrefraction.

In some embodiments, a method of creating an optical device with avariable index of refraction for angular selectivity comprisesdepositing a film on a substrate; patterning the film to create anoptical structure; and/or exposing the optical structure to an energygradient, as part of a process to form a refractive-index gradient inthe optical structure corresponding to the energy gradient. In someembodiments, the process further comprises exposing the opticalstructure to a compound as part of the process to form therefractive-index gradient; forming an overcoat on the optical structure;using a gray-tone mask and ultra-violet (UV) light to form a lightgradient (e.g., dose up to 10 J/cm²; and/or from 0.1-100 J/cm²);exposing the film to flood UV light; and/or depositing a moiety that hasa lower refractive index than the film; incorporating a depolymerizableoligomer or polymer into the film. In some embodiments, the compound hasa higher refractive index than the film had before the film is exposedto the compound; the optical structure is a grating; the film is animprint resist; the patterning the film comprises imprinting the filmwith a template to create the optical structure; the film is aphotoresist; patterning the film comprises using photolithography toremove at least a portion of the film to form the optical structure; thefilm comprises a reactive monomer; the film comprises a photoacidgenerator; the energy gradient is a thermal gradient; the energygradient is a light gradient; the film comprises a metal oxide sol-gelprecursor; and/or the energy gradient is a thermal gradient produced bya hot plate (e.g., temperatures ranging from 25 to 350° C.). In someembodiments, the optical structure is a grating, and the method furthercomprises integrating the grating into a device used in a virtualreality and/or an augmented-reality system, wherein: the virtual realityand/or the augmented-reality system comprises: an optical source, awaveguide, an optical coupler configured to couple light from theoptical source into the waveguide, and an output coupler configured tocouple light out of the waveguide; the waveguide is a planar waveguide;and the grating is part of the output coupler.

In some embodiments, a method of creating an optical device with avariable index of refraction for angular selectivity comprisesdepositing a film on a substrate; exposing the film to UV light using agray-tone mask; developing the film using a solvent to create a variablerefractive index in the film; and/or patterning the film to create anoptical structure after developing the film. In some embodiments, thefilm is a block copolymer and/or patterning the film comprises applyinga photoresist to the film, exposing the photoresist, partially removingthe photoresist based on applying the photoresist, and/or etching thefilm to create the optical structure.

In some embodiments, a device used in a virtual reality and/or anaugmented-reality system comprises an optical source; a waveguide,wherein the waveguide is a planar waveguide; an optical couplerconfigured to couple light from the optical source into the waveguide;an output coupler configured to couple light out of the waveguide;and/or a grating, as part of the output coupler, wherein the grating hasa varying refractive index.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments are described with reference to the followingfigures.

FIG. 1 is a diagram of an embodiment of a near-eye display.

FIG. 2 is an embodiment of a cross section of the near-eye display.

FIG. 3 illustrates an isometric view of an embodiment of a waveguidedisplay with a single source assembly.

FIG. 4 illustrates a cross section of an embodiment of the waveguidedisplay.

FIG. 5 is a block diagram of an embodiment of a system including thenear-eye display.

FIG. 6 is a block diagram of an embodiment of an output coupler withangular selectivity.

FIG. 7 illustrates an embodiment of imprinting a film using a templateto form an optical structure.

FIG. 8 illustrates an embodiment of masking a photoresist.

FIG. 9 illustrates an embodiment of a gradient of concentrations of astrong acid in an optical structure.

FIG. 10 illustrates an embodiment of the optical structure exposed to acompound.

FIG. 11 illustrates an embodiment of an optical structure with arefractive-index gradient that is enhanced.

FIG. 12 illustrates an embodiment of an imprint resist comprising asol-gel precursor.

FIG. 13 illustrates the imprint resist comprising the sol-gel precursorexposed to a thermal gradient.

FIG. 14 illustrates an embodiment of a block copolymer film deposited ona substrate.

FIG. 15 illustrates an embodiment of developing domains in the blockcopolymer film exposed to UV light using a gray-tone mask.

FIG. 16 illustrates an embodiment of a pattern of photoresist on theblock copolymer film.

FIG. 17 illustrates an embodiment of the pattern of the photoresisttransferred to the block copolymer film.

FIG. 18 illustrates an embodiment of a flowchart of a process forcreating an optical device with a variable refractive index using anenergy gradient.

FIG. 19 illustrates an embodiment of a flowchart of a process forcreating an optical device with a variable refractive index usinglithography and infusion.

FIG. 20 illustrates an embodiment of a flowchart of a process forcreating an optical device with a variable refractive index usinglithography and a sol-gel precursor.

FIG. 21 illustrates an embodiment of a flowchart of a process forcreating an optical device with a variable refractive index usinglithography and block-copolymer degradation.

The figures depict embodiments of the present disclosure for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated may be employed without departing from theprinciples, or benefits touted, of this disclosure.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, specificdetails are set forth in order to provide a thorough understanding ofcertain inventive embodiments. However, it will be apparent that variousembodiments may be practiced without these specific details. The figuresand description are not intended to be restrictive.

This disclosure relates generally to optical devices. More specifically,and without limitation, this disclosure relates to optical deviceshaving a refractive index that varies. In some embodiments, a gratingstructure with a variable refractive index is useful as an outputcoupler of a waveguide. A variable refractive index grating can beproduced by multiple lithographic exposures to: 1) define the gratingstructure, and/or 2) define a concentration of gradient of chemicallyreactive sites that can be modified with high or low refractive indexcompounds after the first lithography step. Variable refractive indexgratings can also be produced by depositing a variable refractive indexfilm of monomeric resin or polymer, which can then be patterned into agrating structure using traditional photolithography, electron-beamlithography, nanoimprint, and/or nanoimprint lithography. The refractiveindex gradient can be produced in either one dimension or two dimensionsin various and/or arbitrary shapes for a gradient profile (e.g., limitedto resolution of photolithography and/or electron-beam lithography).

FIG. 1 is a diagram of an embodiment of a near-eye display 100. Thenear-eye display 100 presents media to a user. Examples of mediapresented by the near-eye display 100 include one or more images, video,and/or audio. In some embodiments, audio is presented via an externaldevice (e.g., speakers and/or headphones) that receives audioinformation from the near-eye display 100, a console, or both, andpresents audio data based on the audio information. The near-eye display100 is generally configured to operate as a virtual reality (VR)display. In some embodiments, the near-eye display 100 is modified tooperate as an augmented reality (AR) display and/or a mixed reality (MR)display.

The near-eye display 100 includes a frame 105 and a display 110. Theframe 105 is coupled to one or more optical elements. The display 110 isconfigured for the user to see content presented by the near-eye display100. In some embodiments, the display 110 comprises a waveguide displayassembly for directing light from one or more images to an eye of theuser.

FIG. 2 is an embodiment of a cross section 200 of the near-eye display100 illustrated in FIG. 1 . The display 110 includes at least onewaveguide display assembly 210. An exit pupil 230 is a location wherethe eye 220 is positioned in an eyebox region when the user wears thenear-eye display 100. For purposes of illustration, FIG. 2 shows thecross section 200 associated with a single eye 220 and a singlewaveguide display assembly 210, but a second waveguide display is usedfor a second eye of a user.

The waveguide display assembly 210 is configured to direct image lightto an eyebox located at the exit pupil 230 and to the eye 220. Thewaveguide display assembly 210 may be composed of one or more materials(e.g., plastic, glass, etc.) with one or more refractive indices. Insome embodiments, the near-eye display 100 includes one or more opticalelements between the waveguide display assembly 210 and the eye 220.

In some embodiments, the waveguide display assembly 210 includes a stackof one or more waveguide displays including, but not restricted to, astacked waveguide display, a varifocal waveguide display, etc. Thestacked waveguide display is a polychromatic display (e.g., ared-green-blue (RGB) display) created by stacking waveguide displayswhose respective monochromatic sources are of different colors. Thestacked waveguide display is also a polychromatic display that can beprojected on multiple planes (e.g. multi-planar colored display). Insome configurations, the stacked waveguide display is a monochromaticdisplay that can be projected on multiple planes (e.g. multi-planarmonochromatic display). The varifocal waveguide display is a displaythat can adjust a focal position of image light emitted from thewaveguide display. In alternate embodiments, the waveguide displayassembly 210 may include the stacked waveguide display and the varifocalwaveguide display.

FIG. 3 illustrates an isometric view of an embodiment of a waveguidedisplay 300. In some embodiments, the waveguide display 300 is acomponent (e.g., the waveguide display assembly 210) of the near-eyedisplay 100. In some embodiments, the waveguide display 300 is part ofsome other near-eye display or other system that directs image light toa particular location.

The waveguide display 300 includes a source assembly 310, an outputwaveguide 320, and a controller 330. For purposes of illustration, FIG.3 shows the waveguide display 300 associated with a single eye 220, butin some embodiments, another waveguide display separate, or partiallyseparate, from the waveguide display 300 provides image light to anothereye of the user.

The source assembly 310 generates image light 355. The source assembly310 generates and outputs the image light 355 to a coupling element 350located on a first side 370-1 of the output waveguide 320. The outputwaveguide 320 is an optical waveguide that outputs expanded image light340 to an eye 220 of a user. The output waveguide 320 receives the imagelight 355 at one or more coupling elements 350 located on the first side370-1 and guides received input image light 355 to a directing element360. In some embodiments, the coupling element 350 couples the imagelight 355 from the source assembly 310 into the output waveguide 320.The coupling element 350 may be, e.g., a diffraction grating, aholographic grating, one or more cascaded reflectors, one or moreprismatic surface elements, and/or an array of holographic reflectors.

The directing element 360 redirects the received input image light 355to the decoupling element 365 such that the received input image light355 is decoupled out of the output waveguide 320 via the decouplingelement 365. The directing element 360 is part of, or affixed to, thefirst side 370-1 of the output waveguide 320. The decoupling element 365is part of, or affixed to, the second side 370-2 of the output waveguide320, such that the directing element 360 is opposed to the decouplingelement 365. The directing element 360 and/or the decoupling element 365may be, e.g., a diffraction grating, a holographic grating, one or morecascaded reflectors, one or more prismatic surface elements, and/or anarray of holographic reflectors.

The second side 370-2 represents a plane along an x-dimension and ay-dimension. The output waveguide 320 may be composed of one or morematerials that facilitate total internal reflection of the image light355. The output waveguide 320 may be composed of e.g., silicon, plastic,glass, and/or polymers. The output waveguide 320 has a relatively smallform factor. For example, the output waveguide 320 may be approximately50 mm wide along x-dimension, 30 mm long along y-dimension and 0.5-1 mmthick along a z-dimension.

The controller 330 controls scanning operations of the source assembly310. The controller 330 determines scanning instructions for the sourceassembly 310. In some embodiments, the output waveguide 320 outputsexpanded image light 340 to the user's eye 220 with a large field ofview (FOV). For example, the expanded image light 340 provided to theuser's eye 220 with a diagonal FOV (in x and y) of 60 degrees and/orgreater and/or 150 degrees and/or less. The output waveguide 320 isconfigured to provide an eyebox with a length of 20 mm or greater and/orequal to or less than 50 mm; and/or a width of 10 mm or greater and/orequal to or less than 50 mm.

FIG. 4 illustrates an embodiment of a cross section 400 of the waveguidedisplay 300. The cross section 400 includes the source assembly 310 andthe output waveguide 320. The source assembly 310 generates image light355 in accordance with scanning instructions from the controller 330.The source assembly 310 includes a source 410 and an optics system 415.The source 410 is a light source that generates coherent or partiallycoherent light. The source 410 may be, e.g., a laser diode, a verticalcavity surface emitting laser, and/or a light emitting diode.

The optics system 415 includes one or more optical components thatcondition the light from the source 410. Conditioning light from thesource 410 may include, e.g., expanding, collimating, and/or adjustingorientation in accordance with instructions from the controller 330. Theone or more optical components may include one or more lens, liquidlens, mirror, aperture, and/or grating. In some embodiments, the opticssystem 415 includes a liquid lens with a plurality of electrodes thatallows scanning a beam of light with a threshold value of scanning angleto shift the beam of light to a region outside the liquid lens. Lightemitted from the optics system 415 (and also the source assembly 310) isreferred to as image light 355.

The output waveguide 320 receives the image light 355. The couplingelement 350 couples the image light 355 from the source assembly 310into the output waveguide 320. In embodiments where the coupling element350 is diffraction grating, a pitch of the diffraction grating is chosensuch that total internal reflection occurs in the output waveguide 320,and the image light 355 propagates internally in the output waveguide320 (e.g., by total internal reflection), toward the decoupling element365.

The directing element 360 redirects the image light 355 toward thedecoupling element 365 for decoupling from the output waveguide 320. Inembodiments where the directing element 360 is a diffraction grating,the pitch of the diffraction grating is chosen to cause incident imagelight 355 to exit the output waveguide 320 at angle(s) of inclinationrelative to a surface of the decoupling element 365.

In some embodiments, the directing element 360 and/or the decouplingelement 365 are structurally similar. The expanded image light 340exiting the output waveguide 320 is expanded along one or moredimensions (e.g., may be elongated along x-dimension). In someembodiments, the waveguide display 300 includes a plurality of sourceassemblies 310 and a plurality of output waveguides 320. Each of thesource assemblies 310 emits a monochromatic image light of a specificband of wavelength corresponding to a primary color (e.g., red, green,or blue). Each of the output waveguides 320 may be stacked together witha distance of separation to output an expanded image light 340 that ismulti-colored.

FIG. 5 is a block diagram of an embodiment of a system 500 including thenear-eye display 100. The system 500 comprises the near-eye display 100,an imaging device 535, and an input/output interface 540 that are eachcoupled to a console 510.

The near-eye display 100 is a display that presents media to a user.Examples of media presented by the near-eye display 100 include one ormore images, video, and/or audio. In some embodiments, audio ispresented via an external device (e.g., speakers and/or headphones) thatreceives audio information from the near-eye display 100 and/or theconsole 510 and presents audio data based on the audio information to auser. In some embodiments, the near-eye display 100 may also act as anAR eyewear glass. In some embodiments, the near-eye display 100 augmentsviews of a physical, real-world environment, with computer-generatedelements (e.g., images, video, sound, etc.).

The near-eye display 100 includes a waveguide display assembly 210, oneor more position sensors 525, and/or an inertial measurement unit (IMU)530. The waveguide display assembly 210 includes the source assembly310, the output waveguide 320, and the controller 330.

The IMU 530 is an electronic device that generates fast calibration dataindicating an estimated position of the near-eye display 100 relative toan initial position of the near-eye display 100 based on measurementsignals received from one or more of the position sensors 525.

The imaging device 535 generates slow calibration data in accordancewith calibration parameters received from the console 510. The imagingdevice 535 may include one or more cameras and/or one or more videocameras.

The input/output interface 540 is a device that allows a user to sendaction requests to the console 510. An action request is a request toperform a particular action. For example, an action request may be tostart or end an application or to perform a particular action within theapplication.

The console 510 provides media to the near-eye display 100 forpresentation to the user in accordance with information received fromone or more of: the imaging device 535, the near-eye display 100, andthe input/output interface 540. In the example shown in FIG. 5 , theconsole 510 includes an application store 545, a tracking module 550,and an engine 555.

The application store 545 stores one or more applications for executionby the console 510. An application is a group of instructions, that whenexecuted by a processor, generates content for presentation to the user.Examples of applications include: gaming applications, conferencingapplications, video playback application, or other suitableapplications.

The tracking module 550 calibrates the system 500 using one or morecalibration parameters and may adjust one or more calibration parametersto reduce error in determination of the position of the near-eye display100.

The tracking module 550 tracks movements of the near-eye display 100using slow calibration information from the imaging device 535. Thetracking module 550 also determines positions of a reference point ofthe near-eye display 100 using position information from the fastcalibration information.

The engine 555 executes applications within the system 500 and receivesposition information, acceleration information, velocity information,and/or predicted future positions of the near-eye display 100 from thetracking module 550. In some embodiments, information received by theengine 555 may be used for producing a signal (e.g., displayinstructions) to the waveguide display assembly 210 that determines atype of content presented to the user.

FIG. 6 illustrates a cross section 600 of an embodiment of a waveguidedisplay with angular selectivity. Angular selectivity addressessystem-level efficiency. Cross section 600 includes the coupling element350, the output waveguide 320, the decoupling element 365, and an eyebox604, wherein the eyebox 604 is at the exit pupil 230. Light travelingfrom the coupling element 350 is transmitted through the outputwaveguide 320 and to the decoupling element 365. Light from thedecoupling element 365 is selectively directed to the eyebox 604. Theeyebox 604 is a usable area of light output from the decoupling element365 at the exit pupil 230. In some embodiments, direction of light fromthe decoupling element 365 is not changed. In some embodiments, anintensity within a particular angular field of view is optimized.Gratings project light over a range of in-coupled angles. Extractionefficiency is increased for a particular field of view that hits theeyebox 604, thus minimizing light that cannot be seen by the eye. Forexample, light intensity distribution between modes of a grating ischanged as a function of x and/or y so that more light is directed in amode of the grating that is within the field of view of the eyebox 604.

Point A, point B, and point C are points along a plane of the decouplingelement 365 where light is transmitted from the decoupling element 365toward the eyebox 604. Point A is opposite point C. Point B is betweenpoint A and point C. The decoupling element 365 is a diffractiongrating. The diffraction grating is configured to selectively changedistribution of light emitted in modes of the diffraction grating. InFIG. 6 , light from point A is primarily distributed in a mode directeddown and to the right; light from point B is primarily distributed in amode directed down (i.e., in a direction normal to the second side 370-2of the output waveguide 320); and light from point C is primarilydistributed in a mode directed down and to the left. Put another way,light from points A, B, and C can be defined by two vectors, a vectornormal to the second side 370-2 and a lateral vector, wherein thelateral vector is orthogonal to the normal vector. The lateral vector oflight from point A points in a direction opposite the lateral vector oflight from point C; and a lateral vector of light from point B is zero(e.g., light from point B is in a direction of the normal vector of thesecond side 370-2). Thus light emitted from the decoupling element 365is selectively directed to the eyebox 604 from point A, point B, andpoint C.

If light from the decoupling element 365 was not angularly directed,light from point A and/or point C would be transmitted in a directionparallel to light transmitted form point B (e.g., as shown in FIG. 4 ),and not as much light would enter the eyebox 604. Thus light from pointB would appear brighter than light from point A and from point C. Thusif an image of a tree were centered in a field of view, a middle of atrunk of a tree might look bright, and leaves at a top of the tree andground near a base of the tee (e.g., parts of a periphery of the image)might appear faded to a user. Parts of the periphery might appear fadedbecause light intensity from pixels of the display 110 in the periphery(e.g., from point A and/or point C) would have less intensity reachingthe eyebox 604 than light intensity from point B. For example, lightfrom a first-order mode of a diffraction grating from points A and Cwould transmit parallel to a z-dimension and not selectively directedinto the eyebox 604. In some embodiments, a lens is used to focus lightfrom point A and/or point C into the eyebox 604. Yet a lens can be heavyto a user. Thus not using a lens, or using a thinner lens, improves auser's experience because the VR set is not as heavy.

In some embodiments, the decoupling element 365 is designed such thatlight from points between point A, point B, and/or point C are alsoselectively directed to the eyebox 604. In some embodiments, the outputcoupler (e.g., decoupling element 365) has a variable refractive index.In some embodiments, the decoupling element comprises a chirped grating(e.g., a grating with variable pitch).

In some embodiments, a system used for a virtual-reality and/or anaugmented-reality display comprises: an optical source (e.g., sourceassembly 310); a waveguide (e.g., output waveguide 320); a couplingelement (e.g., coupling element 350) configured to couple light from theoptical source into the waveguide; and/or a decoupling element (e.g.,decoupling element 365) configured to couple light out of the waveguide,wherein the decoupling element an optical element with a variablerefractive index. The variable refractive index is configured toselectively direct light (e.g., modify light intensity) from thedecoupling element 365 to the eyebox 604.

In some embodiments, an angular position of diffraction orders isdefined by a period of a grating, wavelength of light, and/or adirection of incoming light. Shape, refractive index, height, and/orduty cycle of the grating do not change the angular position of thediffracted orders but can determine a distribution of energy indiffraction orders. To control a brightness, a uniformity, a field ofview (FOV), and/or efficiency of an image projected to an eye of a user,design variables (e.g., grating period, wavelength of light, directionof incoming light, shape, refractive index, and/or duty cycle) of inputand/or output diffraction gratings in a waveguide-based AR display canbe controlled and/or varied across a pupil expander. In someembodiments, the output waveguide 320 is a planar waveguide (e.g., asopposed to a fiber-optic waveguide). In some embodiments, the device isdefined by a length, and the refractive index gradient changesmonotonically from high to low over the length of the device.

FIG. 7 illustrates an embodiment of imprinting a film using a template705 to form an optical structure 710. The film is deposited on asubstrate 715 (e.g., spin coating). In some embodiments, the substrate715 is a semiconductor substrate. The film is a resist (e.g., an imprintresist configured to hold a shape after being pressed by the template705). The template 705 is a nano-imprint. The template 705 is defined bya pattern that when pressed into the film transfers the pattern to thefilm to form the optical structure 710. In some embodiments, the patternis to make a grating for the coupling element 350, the directing element360, and/or the decoupling element 365.

FIG. 8 illustrates an embodiment of masking a photoresist. In someembodiments, a photoresist 805 is used in lieu of, in addition to, or incombination with an imprint resist as described in FIG. 7 . Thephotoresist 805 is spun onto a substrate 715. A mask 810 is used toexpose a pattern in the photoresist 805. The photoresist is developedand/or etched to form an optical structure based on the pattern (e.g., adiffraction grating).

In some embodiments, the photoresist 805 is a polymer that comprises aphotoacid generator. The photo acid generator forms a strong acidcompound during an initial lithography step and/or during a subsequentexposure step. Absorbance of the photoacid generator and an exposurewavelength can be tuned to activate the photoacid generator during theinitial lithography step and/or during the subsequent exposure step. Insome embodiments, electron-beam lithography is used to form the patternin the photoresist in lieu of, or in addition to, using the mask 810.

In some embodiments, the photoresist 805 contains a reactive monomer,such as tert-butoxy acrylate, that can be deprotected with strong acidduring an annealing step (˜100° C.). The reaction between the monomerand strong acid produces a residual reactive functional group (such as acarboxylic acid), which is capable of selectively reacting with a highrefractive index compound, such as titanium butoxide, in a laterprocessing step.

FIG. 9 illustrates an embodiment of a gradient of concentration of astrong acid in an optical structure 910. The optical structure 910 is aon a substrate 715. In some embodiments, the optical structure 910 isformed from a film (e.g., using an imprint resist as described in FIG. 7and/or using a photoresist as described in FIG. 8 ). The concentrationof strong acid is lower on the left (lighter in the figure) and higheron the right (darker in the figure).

To obtain the gradient of concentrations of the strong acid, the opticalstructure 910 was exposed to an energy gradient. The energy gradient canbe a thermal gradient and/or an optical gradient. A refractive-indexgradient is formed in the structure 910 based on exposing the opticalstructure 910 to the energy gradient.

In some embodiments, the optical structure 910 is exposed to a gradientof light. The gradient of light exposes the optical structure 910 tovariable light doses (e.g., using gray-tone mask). By exposing theoptical structure 910 to the gradient of light, the gradient ofconcentration of the strong acid is formed. The gradient ofconcentration of the strong acid produces a gradient of reactivefunctional groups during a later annealing step. As the strong acid isannealed, it reacts with a monomer to increase the refractive index ofthe film.

In some embodiments, the optical structure 910 is exposed to a uniformdose of light across the optical structure 910, but annealed atdifferent temperatures using a thermal gradient hot plate. Since theextent of reaction between the strong acid and the reactive monomerdepends on temperature, a concentration gradient of reactive functionalgroups is created that follows the temperature gradient from annealing.A shape of the concentration gradient of the strong acid can be adjustedby utilizing a photoresist with multiple reactive monomers that can bedeprotected at different temperatures. In some embodiments, exposing theoptical structure 910 to an energy gradient produces a better resolutiongradient than using drops of resin from an inkjet.

FIG. 10 illustrates an embodiment of the optical structure 910 exposedto a compound. The compound has a higher refractive index than the filmof the optical structure 910. The compound selectively reacts with thereactive functional groups. In some embodiments, the compound containsorganometallic moieties, which are precursors to metal oxides such astitanium oxide, hafnium oxide, zirconium oxide, etc.

In some embodiments, the optical structure 910 is exposed toorganometallic compounds in vapor phase and/or in liquid phase. Forvapor phase reactions, the organometallic compound diffuses throughout apolymer matrix and reacts selectively with the deprotected monomersites. For liquid phase reactions, the resist is exposed to anorganometallic/solvent mixture, which is capable of swelling the resistwithout dissolving it. After exposure, the film of the optical structure910 can be subsequently processed by annealing and/or exposure to watervapor to complete formation of metal oxide in the film. Because therefractive index of the metal oxide is higher than the film beforeprocessing, a refractive-index gradient is created in the opticalstructure 910.

The optical structure 910 is defined by a first end 1010-1 and a secondend 1010-2. The optical structure 910 has a low refractive index n₁ anda high refractive index n₂. A refractive-index difference Δn=n₂ minusn₁. In some embodiments, the optical structure 910 in FIG. 10 has thefollowing properties: n₁=1.4-1.6, 1.45-1.55, 1.5, and/or 1.5±3, 5,and/or 10%; n₂=1.65-1.85, 1.7-1.8, 1.75, and/or 1.75±3, 5, and/or 10%;and/or Δn=0.15-0.35, 0.2-0.3, and/or 0.25±3, 5, and/or 10%.

FIG. 11 illustrates an embodiment of an optical structure 910 with arefractive-index gradient that is enhanced. The refractive-indexgradient of the optical structure 910 can be enhanced by one or moreadditional processing steps. In some embodiments, the optical structure910 is exposed to flood UV light. The flood UV light de-protectsremaining reactive monomers in the film of the optical structure 910.The flood UV light exposure is followed by a second deposition of amoiety having a lower refractive index (e.g., a fluorinated compound),which selectively reacts with sites created by the flood UV lightexposure. The flood UV light exposure and deposition of the moietyincrease the refractive index difference Δn, by lowering n₁.

In some embodiments, the refractive index of the film of the opticalstructure 910 is lowered by incorporating a depolymerizable oligomer orpolymer into the film (e.g., poly(propylene glycol) orpoly(phthalaldehyde)), which decomposes upon reaction with light orstrong acid. Voids left in the film after the decomposition lower therefractive index of the film.

In some embodiments, n₁=1.25-1.45; 1.3-1.4, and/or 1.35±3, 5, and/or10%; n₂ of FIG. 11 =n₂ of FIG. 10 ; and/or Δn=0.35-0.45 and/or 0.4±3, 5,and/or 10%. In some embodiments, an optical device is characterized by afirst end 1010-1, a second end 1010-2 opposite the first end, and/or arefractive index change. In some embodiments, the refractive indexchange is a monotonic function. In some embodiments, the optical deviceis on a substrate 715. In some embodiments, the optical device is agrating.

FIG. 12 illustrates an embodiment of an imprint resist comprising asol-gel precursor. A film 1210 is applied to a substrate 715. The filmcomprises a sol-gel precursor. In some embodiments, the film comprises amonomeric or polymeric resist containing a metal oxide sol-gelprecursor, such as titanium butoxide. The film 1210 is patterned usingthe template 705 to form an optical structure (e.g., a grating). In someembodiments, the film 1210 is patterned using photolithography and/orelectron-beam lithography (e.g., as described in FIG. 8 ).

FIG. 13 illustrates the imprint resist comprising the sol-gel precursorexposed to a thermal gradient. The substrate 715 is put in thermalcontact with a hot plate 1305. The film is subsequently baked using thehot plate 1305 having a thermal gradient. In regions of the film 1210baked at higher temperatures, an extent of the sol-gel reaction isgreater and produces higher concentrations of high refractive indexmetal oxide. The metal oxide concentration gradient directly produces arefractive index gradient in the film 1210.

FIG. 14 illustrates an embodiment of a block copolymer film deposited ona substrate. A film 1410 is deposited on a substrate 715 (e.g., by spincoating). The film 1410 is a thin film of a block copolymer (BCP), suchas poly(styrene-block-methyl methacrylate) (PS-b-PMMA). The film 1410 isannealed to produce self-assembled block copolymer domains (e.g.,hexagonally-packed cylinders).

FIG. 15 illustrates an embodiment of developing domains in the blockcopolymer film exposed to UV light using a gray-tone mask. The film 1410is exposed to UV light, which decomposes the PMMA block and crosslinksthe PS block. The UV exposure is done using a grey tone mask, whichcreates a gradient of exposure dose for the film 1410. The film 1410 issubsequently developed using a selective solvent for the degraded PMMAdomains, such as acetic acid or isopropanol. In areas exposed to more UVlight, more of the PMMA domains are developed. Voids left by thedeveloped PMMA lowers the refractive index of the film 1410.

FIG. 16 illustrates an embodiment of a pattern of photoresist on theblock copolymer film. The film 1410 can be converted into an opticalstructure by overcoating a photoresist 1605 or imprint resin, patterningthe photoresist 1605 using photolithography, electron-beam lithography,and/or imprint lithography. In some embodiments, this process can alsobe generalized to other materials capable of generating a variablerefractive index (e.g. sol-gel materials and films with depolymerizablemoieties). In some embodiments, the sol-gel precursor is a metalalkoxide having the structure M+OR— (where M+ can be titanium, hafnium,zirconium, tantalum, niobium, aluminum, or other transition metalscapable of forming alkoxides, and/or is an alkoxide with any isomer ofmethyl, ethyl, isopropyl, or butyl side chains); and/or a monomer is anacrylate or epoxide-functionalized carboxylic acid (such as acrylicacid) or β-keto ester.

FIG. 17 illustrates an embodiment of the pattern of the photoresisttransferred to the block copolymer film. The pattern of the photoresist1605 is transferred to the film 1410 (e.g., by etching).

FIG. 18 illustrates an embodiment of a flowchart of a process 1800 forcreating an optical device with a variable refractive index using anenergy gradient. Process 1800 begins in step 1804 with depositing a filmon a substrate. Examples of film are given in descriptions correspondingto FIGS. 7, 8, 12, and 14 . In step 1808, the film is patterned tocreate an optical structure. Examples of pattering a film to form anoptical structure are given in descriptions corresponding to FIGS. 7, 8,12, 16, and 17 . In step 1812, the optical structure is exposed to anenergy gradient to form a refractive-index gradient in the opticalstructure. Examples of energy gradients are light gradients and thermalgradients. Examples of exposing a structure and/or film to an energygradient are given in descriptions corresponding to FIGS. 9-11, 13, and15 .

In some embodiments, the process 1800 further comprises exposing theoptical structure to a compound as part of the process to form therefractive-index gradient; forming an overcoat on the optical structure;using a gray-tone mask and UV light to form a light gradient; exposingthe film to flood UV light; depositing a moiety that has a lowerrefractive index than the film; and/or incorporating a depolymerizableoligomer or polymer into the film. In some embodiments, the compound hasa higher refractive index than the film had before the film is exposedto the compound; the optical structure is a grating; the film is animprint resist; the patterning the film comprises imprinting the filmwith a template to create the optical structure; the film is aphotoresist; patterning the film comprises using photolithography toremove at least a portion of the film to form the optical structure; thefilm comprises a reactive monomer; the film comprises a photoacidgenerator; the energy gradient is a thermal gradient; the energygradient is a light gradient; the film comprises a metal oxide sol-gelprecursor; and/or the energy gradient is a thermal gradient produced bya hot plate. In some embodiments, the optical structure is a grating,and the method further comprises integrating the grating into a deviceused in a virtual reality and/or an augmented-reality system, wherein:the virtual reality and/or the augmented-reality system comprises: anoptical source (e.g., source 410), a waveguide (e.g., output waveguide320), an optical coupler (e.g., coupling element 350) configured tocouple light from the optical source into the waveguide, and/or anoutput coupler (e.g., decoupling element 365) configured to couple lightout of the waveguide; the waveguide is a planar waveguide; and/or thegrating is part of the output coupler.

FIG. 19 illustrates an embodiment of a flowchart of a process 1900 forcreating an optical device with a variable refractive index usinglithography and infusion. Process 1900 begins in step 1904 with creatinga grating structure (e.g., FIG. 7 and/or FIG. 8 ). In some embodiments,a template is used to define a grating structure in an imprint resist,and/or lithography is used define the grating structure. In someembodiments, the grating structure contains a reactive monomer, whichcan be de-protected with strong acid during annealing. In someembodiments, the grating structure comprises a photo-acid generator. Thephoto-acid generator can be activated by exposure to light.

In step 1908, the grating structure is exposed to an energy gradient.Exposing the grating structure to light and/or temperature de-protectsites. In some embodiments, the grating structure is exposed to avariable dose of light and/or to a uniform does of light and annealed todifferent temperatures (e.g., FIG. 9 ). In step 1912, the gratingstructure is exposed to a compound with a high refractive index. Thecompound reacts selectively with the de-protected sites to create arefractive index variance in the grating (e.g., FIG. 10 ).

In step 1916, the refractive index variance is optionally enhanced(e.g., FIG. 11 ) by one or more further steps. Examples of further stepsto enhance the refractive index variance include: flood UV exposure, tode-protect remaining monomers; a deposition of low refractive indexmoiety, which selectively reacts with the de-protected sites produced bythe flood UV exposure; and/or incorporating a depolymerizable oligomeror polymer into the film, which decomposes upon reaction with light orstrong acid and voids (e.g., air) left after the reaction lower therefractive index of the grating structure because voids have a lowrefractive index (e.g., air refractive index is ˜1).

FIG. 20 illustrates an embodiment of a flowchart of a process 2000 forcreating an optical device with a variable refractive index usinglithography and a sol-gel precursor. Process 2000 begins in step 2004with creating a grating in a film (e.g., FIG. 12 ). In some embodiments,the film is applied to a substrate and the grating structure is createdusing nano imprint, photolithography, and/or electron-beam lithography.The film comprises a sol-gel precursor.

In step 2108, the grating structure is baked (e.g., FIG. 13 ). Thegrating is baked using a hot plate with a temperature gradient. Areas ofthe grating structure exposed to higher temperatures produce higherconcentrations of a metal oxide. The metal oxide has a higher refractiveindex than the film before baking.

FIG. 21 illustrates an embodiment of a flowchart of a process 2100 forcreating an optical device with a variable refractive index usinglithography and block-copolymer degradation. Process 2100 begins in step2104 with depositing a film on a substrate (e.g., FIG. 14 ). The film isa block copolymer. The film is exposed to a light gradient (e.g., FIG.15 ). In some embodiments, a UV light with a gray-tone mask is used. Instep 2112, the film is developed. In some embodiments, a selectivesolvent is used to develop the film. In areas exposed to more UV light,more PS-b-PMMA (poly styrene-block-methyl methacrylate) domains aredeveloped. Voids left by the developed PMMA lower the refractive index.In step 2116, an optical structure is created in the film (e.g., FIGS.16 and 17 ).

Embodiments of the invention may include or be implemented inconjunction with an artificial reality system. Artificial reality is aform of reality that has been adjusted in some manner beforepresentation to a user, which may include, e.g., a virtual reality (VR),an augmented reality (AR), a mixed reality (MR), a hybrid reality, orsome combination and/or derivatives thereof. Artificial reality contentmay include completely generated content or generated content combinedwith captured (e.g., real-world) content. The artificial reality contentmay include video, audio, haptic feedback, or some combination thereof,and any of which may be presented in a single channel or in multiplechannels (such as stereo video that produces a three-dimensional effectto the viewer). Additionally, in some embodiments, artificial realitymay also be associated with applications, products, accessories,services, or some combination thereof, that are used to, e.g., createcontent in an artificial reality and/or are otherwise used in (e.g.,perform activities in) an artificial reality. The artificial realitysystem that provides the artificial reality content may be implementedon various platforms, including a head-mounted display (HMD) connectedto a host computer system, a standalone HMD, a mobile device orcomputing system, or any other hardware platform capable of providingartificial reality content to one or more viewers.

The foregoing description of the embodiments of the disclosure has beenpresented for the purpose of illustration; it is not intended to beexhaustive or to limit the disclosure to the precise forms disclosed.Persons skilled in the relevant art can appreciate that manymodifications and variations are possible in light of the abovedisclosure. For example, the energy gradient can be a gradient intwo-dimensions (e.g., in a parabola shape). In some embodiments, ahigh-temperature tag (e.g., an acid generator) is put in the film. Insome embodiments, a photo-base generator is put in and acid is generatedeverywhere. Light is shined from the second end 1010-2 to activate theacid. Light is shined from the first end 1010-1 to active the base.

Some portions of this description describe the embodiments of thedisclosure in terms of algorithms and symbolic representations ofoperations on information. These algorithmic descriptions andrepresentations are commonly used by those skilled in the dataprocessing arts to convey the substance of their work effectively toothers skilled in the art. These operations, while describedfunctionally, computationally, or logically, are understood to beimplemented by computer programs or equivalent electrical circuits,microcode, or the like. Furthermore, it has also proven convenient attimes, to refer to these arrangements of operations as modules, withoutloss of generality. The described operations and their associatedmodules may be embodied in software, firmware, and/or hardware.

Steps, operations, or processes described may be performed orimplemented with one or more hardware or software modules, alone or incombination with other devices. In some embodiments, a software moduleis implemented with a computer program product comprising acomputer-readable medium containing computer program code, which can beexecuted by a computer processor for performing any or all of the steps,operations, or processes described.

Embodiments of the disclosure may also relate to an apparatus forperforming the operations described. The apparatus may be speciallyconstructed for the required purposes, and/or it may comprise ageneral-purpose computing device selectively activated or reconfiguredby a computer program stored in the computer. Such a computer programmay be stored in a non-transitory, tangible computer readable storagemedium, or any type of media suitable for storing electronicinstructions, which may be coupled to a computer system bus.Furthermore, any computing systems referred to in the specification mayinclude a single processor or may be architectures employing multipleprocessor designs for increased computing capability.

Embodiments of the disclosure may also relate to a product that isproduced by a computing process described herein. Such a product maycomprise information resulting from a computing process, where theinformation is stored on a non-transitory, tangible computer readablestorage medium and may include any embodiment of a computer programproduct or other data combination described herein.

The language used in the specification has been principally selected forreadability and instructional purposes, and it may not have beenselected to delineate or circumscribe the inventive subject matter. Itis therefore intended that the scope of the disclosure be limited not bythis detailed description, but rather by any claims that issue on anapplication based hereon. Accordingly, the disclosure of the embodimentsis intended to be illustrative, but not limiting, of the scope of thedisclosure, which is set forth in the following claims.

What is claimed is:
 1. A method of creating an optical device with avariable index of refraction for angular selectivity, the methodcomprising: depositing a film on a substrate, wherein the film includesa block copolymer; exposing the film to ultra-violet (UV) light using agray-tone mask; developing the film using a solvent to create a variablerefractive index in the film; and patterning the film to create anoptical structure after developing the film.
 2. The method of claim 1,wherein depositing the film comprises: spin-coating the film on thesubstrate; and annealing the film to produce self-assembled blockcopolymer domains.
 3. The method of claim 1, wherein the film includespoly(styrene-block-methyl methacrylate) (PS-b-PMMA).
 4. The method ofclaim 3, wherein exposing the film to UV light decomposes poly(methylmethacrylate) (PMMA) blocks in the film.
 5. The method of claim 3,wherein developing the film using the solvent develops more PS-b-PMMAdomains in areas of the film exposed to more UV light.
 6. The method ofclaim 1, wherein exposing the film to the UV light comprises exposingthe film to UV light having a dose between 0.1 and 100 J/cm².
 7. Themethod of claim 1, wherein the solvent includes acetic acid orisopropanol.
 8. The method of claim 1, wherein patterning the filmcomprises: applying a photoresist to the film; selectively exposing thephotoresist; partially removing the photoresist based on selectivelyexposing the photoresist; and etching the film to create the opticalstructure.
 9. The method of claim 1, wherein the optical structureincludes an optical grating.